1. Stairs Terminology and Design Rules

2. Why Stairs Important consideration in a structure
design
function
Accommodate traffic flow from one level to another
Key to circulation in a plan
Code requirements
based upon safety
established by occupant count

3. Stair Groupings based on Material
1--Wood
2--Steel
3--Concrete

4. Types of Stairs Basic types straight run right angle or “L” double “L”
reverse or “U”
winder
spiral or curved

5. Straight Run does not change direction
typical width is 3’-0” to 3’-6” (residential)
typical width for commercial construction is set by code
simple
popular

6. Right Angle or “L” Intermediate platform between floors
A 90 degree directional change occurs, usually near the center
Platform at directional change of stairs
Platform provides a resting area between flights of stairs
Platform

7. Double “L”
Same as “L” but with multiple platforms
Platform
Platform

8. Reverse or U A 180 degree directional turn occurs, usually near center
Platform at direction change
Platform length is 2 (x) stair width
Platform

9. Winder Wedge shape steps Steps continue in place of landing
Unsafe at the small of the wedge
The design: arc in the area of the winder is half the stair width and the tread design is 10”
10” tread
width

10. Spiral and Curved Spiral Stairs Curved Stairs
Used as an additional stair--not used as the main stairs, follow code requirements
Used for unique design with requirements such as
limited or tight spaces
aesthetics
extra/addition stairs
Curved Stairs

11. Stair Terminology Total Rise vertical distance between floors
Run/Unit Run (design run)
horizontal distance from riser to riser, horizontal member
Total Run
horizontal distance between first and last riser
Rise/Unit Rise (design rise)
vertical distance between stairs/treads, vertical member
Rise
total rise
Run
total run

12. Stair Terminology Landing
“floor” at the bottom and top of a flight of stairs
Headroom
vertical distance from outside edge of step (nosing) to ceiling
headroom
stringer
landing
Stringer/Carriage/Stair Jack
member on which risers and treads rest, provides structural support for risers and treads

13. Stair Terminology Nosing Tread Riser projection of tread beyond riser
usually 1 1/8”
Tread
equal to unit run + nosing
Riser
equal to unit rise

14. Stair Terminology Plain Stringer Closed/Housed Stringer
notched out 2x12 to support the treads and risers
Closed/Housed Stringer
stairs ends at stringer and are not exposed, stringer usually routed so the treads and risers will fit into it

15. Stair Terminology at a glance
Run (Unit Run)
Rise (Unit Rise)
Total run
Total rise
Tread
Riser
Nosing
Stringer (carriage)
Headroom
Clearance
Stairwell
Landing (fin fl)
Kick board

16. Stairs Framing Terms double header double trimmer stringers
joist hangers
stairwell

17. Design Considerations
Stairs should be comfortable to climb
degree angle is optimum to prevent fatigue
Max of 16 steps between landings
Design rules have been developed with years of study and experimentation

18. Design Considerations
Every step should be same size
Absolute minimum ratio of riser to tread
4” riser with 11” tread
Absolute maximum ratio of riser to tread
7” riser with no maximum tread
Optimum ratios
7” riser (unit rise)
11” tread (unit run)
includes nosing

19. Design Rules Riser + Tread = 17” - 17 1/2” [book] (17”- 18” usually)
2 (x) Riser + Tread = 24” - 25”
Riser (x) Tread = sq inches

20. Design Rule Example Normal conditions 7 + 10=17 (required 17 to 18)
If: Riser = 7 and Tread = 10
7 + 10= (required 17 to 18)
2 x = (required 24 to 25)
7 x 10 = (required 70 to 75)
All conditions conform to rules

21. Design Rule Example A minimum condition
If: Riser = 5 and Tread = 14
= 19 (required 17 to 18)
2 (x) = 24 (required 24 to 25)
5 (x) 14 = 70 (required 70 to 75)
Only two rules are satisfied, okay since at least one rule works

22. Stair Calculations
Necessary to determine exact riser height and total run
1. determine vertical distance between finished floors
2. divide vertical distance by approximate desired riser height to set approximate number of risers
3. round to number of whole risers
4. divide vertical distance by number of risers to get actual riser height
5. number of unit runs = number or unit rise minus 1
6. Total run: use design rule to determine unit run size then multiply by the number of unit runs

23. Stair Calculations Example
Given: vertical distance = 102”
1--approx # unit rise = 102 / 7.5 = 13.6
2--round 13.6 to 14
3--unit rise height = 102 / 14 = 7.286”
4--14 unit rise (-) 1 = 13 unit runs
5--design rule: R + T =
(therefore) T = (then) T = 10”
6--total run = 10 * 13 = 130” = 10’-10”
Solution: ” and ”

24. Example of a Wood Stair Section

25. Example of an Exterior Concrete Stair Section

26. Stair Section A A--Section View B1 B--Structural Connection Details B2
Scale of sectional drawing (1/2” = 1’-0”)
Coordinate sectional view with details (notations)
B--Structural Connection Details
Scale of detail drawings: 1”= 1’-0” Details to draw
1) top of stair run
2) intermediate landings/platforms
3) bottom of stair run (More) B1 B2 B3

27. Stair Section View Add height and width of platform Add 2x4 kick board
Add 2x6 platform (down steps area)
Determine number and size of Riser and Tread include on your drawing in a note
Show total run on each flight of stairs (More)

28. Structural Connection Details scale 1”=1’-0”
Detail at Top of Stair connection
note use of joist hanger

29. Structural Connection Details
Stringer to Landing connection
note use of ledger
Add platform joist spacing 16”OC
2x6 Ledger
2x4 ledger beyond (hidden lines) (More)

30. Structural Connection Details
Bottom of Stair connection
note 2 x 4 plate (kick board) & notched stringer
Joist are 16” OC

31. ASSIGNMENT On sheet A-7 create the stair cross section A/A-7 and B/A-7
Develop a landing detail 1/A-7
Develop a bottom of stair detail 2/A-7
Develop a top of stair detail 3/A-7
Include handrail information on any or all of the above